When someone or something is very silly/sillier than normal. mostly used on characters or people. Its also normal to write ":3" after. its also meant to be said in a high pitch tone for added silliness
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.